Carburetor



Oct. 1 1957 L. c. DERMOND 2,808,244

cARBuREToR Filed June 2:5, 1954 2 76 lo 2 8O 74 E I I .I 78 g l L A 12 l88 1o 8 a2 24 so 28 n y 5e 26' *44 n 54 4o 4 56 4 42 64 l2 A l v 4s leIt es I as f ,I efe ,fsf M F192 m K l 1 l )QW 93 loo i o "i \m `92INVENToR. 98 i '04 Lawrence' C. Dermond a IOGBY l |02 611g Wifi/nd losCARBRETOR Lawrence lC. Dermond, Rochester, N. Y., assignor to GeneralMotors Corporation, Detroit, Mich., a corporation of DelawareApplication Jne 23, 1954,-"SeiialNo. 438,771 s claims. (ci. 261-39) Thisinvention relates to carbiiretors -for internal combustion engines,particularly engines for automotive vehicles 'and more specifically toautomatic choke mechanism operable to automatically controlthe-positionof an airinlet valve, in order to regulate the air-and fuel ratiothermostatwhich exerts a force tohold the valve closed at lowtemperatures, and by a suction-operated piston responsive to variationsin'suction posterior to the throttle and Iexerting a force tending to`openthe valve as the suction increases.

Devices of this Vkind are Valso old in which a given change intemperature or engine suctiondoes not produce the same movement of thechoke valve Vthroughout the entire range of movement ofsaid valve. Inother words, if 'the temperature increases a given number of degrees andthe suction increases a given number of inches of mercury, the movementof -the valve effected by such changes is different if'the changes occurwhen the valve is Yin one part of its range-of movement than if thevalve is in Va different part of-its range ofmovement when such changesoccur.

Devices Aof this kind are provided because characteristcs of differentengines vary and with some engines, for example, it is desirable to movethe choke valve more rapidly toward open'position upon a vgiven increasein temperature and suction, when the valve is in a certain part of itsoperating range-than it is with other-engines. `For example, it may bedesirable, with some engines, to move the valve more slowly toward openposition irnmediately after the engine has been started and is warmingup than ywith other engines because some 4engines require Ia richermixture for best operation under such conditions than do other engines.

It is the primary object or purpose of this-invention vto provide'in acarburetor an automatic-chokevalve which is controlled by variations intemperature and engine suction and novel means for moving such chokevalve in States Patent response to variations in 'these `factors `at-such different rates per unit of change therein that its movementthroughout Vits operating range will be such as to obtain the mixtreratiobest suited for operation of'a'particular engine.

More particularly, it is an object ofthe invention `to provide acarburetor having an automatic choke valve of the character described,themovementofwhich toward open position be relatively retardedimmediately after its initial movement'which occurs' Whenthe enginestarts to run under its own power', and which Willsubsequently be movedmore rapidly afterth'e valve is opened Ipiston ineffective to move 'thevalve.

to a predetermined extent, and novel means for effecting these movementsof the valve.

According tothe presentinvetition, the objects thereof are accomplishedby the provision'of a suction operated piston connected to the chokevalve and subject rto the effect of suction in the'engine-intakepassagerposterior to the throttle when the valve is in closed position,so that immediately `after the engine starts torun under its ownYpower'the valve is moved, by suction effective on such to thethermostathousing througha constantly open passage and draws "heated 'air throughsaid housing to heat up the thermostat 'and 'bring 'abouttheabove-described motion of the valve during the engine Vwarm-up period.As the choker valve -opens the suction operated piston, 'which isconnected to said valve and 'moves vwith it,rst 'substantially blocks"the passage through which sliction is communicatedto :the end of -the1` iston,-to'render the Then as theV choke valve moveson'further-towa'rdopenY position, a second passage leading to -thetherm`ostat`-housing is placed in communication with =the suctionpassageat `a Vpredeterminedopen `position of theehoke valve.

`After the chokevalve reaches-.this position, the heatingofthe-thermostat-ismuch more rapid than previously, so that thernalmovement ofthe choke valve to full-open position is considerablyfaster-than.thelm'ovement of such valve during `the intermediate portionof its range of movemennafter ythe `effect .of suction 4on the pistonhas become substantially ineffective and before the second passage tothe thermostat housing isfopened.

Further objects .and advantages `of the :present invention will beapparent from the followingdescription, 'reference being .had to theaccompanying-drawings wherein a-preferred embodiment ofthe presentinvention is clearly shown.l f

In the drawings:

Figure 1 isa vertical section, partlyin elevation, of a conventionaldown-draft carburetor embodying they present invention; and v Figure 2is a detail section on the line 2 2 of Figure l.

The carburetor shown in the-drawings is, in general, of conventionalconstruction and lsubstantially the same as that shown inthe copendingapplication of -Elmer Olson, S. N. 192,035, ledOctober 25, 1950,` nowPatent No. 2,698,168 dated Dec. 28, 1954, and comprises three castings2,- 4 and 6 AsuitablyV secured together by screws 8,-or in jany suitableway. n The casting-2 is the air inlet `casting having apassage 10 for.admission of air. The

-casting4 is theA fuel chamber casting and has a constant level fuelchamber 12 therein, in which vfuel is maintained at a substantiallyconstant level mechanismhwhich Will be very briefly described later. Thepassage 10 communicates with a chamber or passage' 14 centrally locatedin the casting 4 into which fuel is yintroduced and which forms themixing chamber ofthe carburetor.

The casting 4 is immediately above and Vsecured to the casting 6 whichis 'the outlet casting 'and is secured in anysiiit'able 'way'to/.theintake manifold of the engine.

iotletlpassage V1'6`is formed in 'the casting 6 and connects with thepassage "14, the 4passages "10, T4 and 16,

forming a continuous intake passage through the carburetor through whichair entering the inlet flows and 1s mixed with fuel to form acombustible mixture which ows through the outlet passage 16 to theengine.

The flow of mixture from the carburetor is controlled by a suitablethrottle Valve 18 secured to a shaft 20 suitably journalled for rotationin the walls of casting 6. This throttle is manually operated in theusual manner by means of an arm 22 secured to one end of the shaft 20and is variably positioned to control the Volume of mixture supplied tothe engine and the speed thereof.

Fuel is supplied to the fuel chamber 12 through-a passage 24 formedinthe wall of casting 2 and communieating with this passage'is anipple-26 threaded in the wall of casting Zand having a passageV 28which conveys fuel from passage 24 to chamber 12. The nipple 26 isenlarged at its lower end to form a cylindrical chamber 30 in which isreceived a'valve 32 which controls ow through passage 28. 'This valve isfreely movable and its lower end rests on a tang 34 cut out from andintegral with a plate or bracket 36 which is secured to a float (notshown), and is pivoted on a pin 38 mounted in lugs 40 which are integralwith and depend from the casting 2 into the chamber 12. When the fueleaches a predetermined level, the float is raised enough to move thevalve 32 against its seat to close passage 28. This is a conventionalfloat valve construction and forms no part of the present invention.

A tube 42 is secured at its upper end in any suitable way to an annularrib 44 projecting from the casting 2 and has a fuel passage 46 formedtherein to convey fuel from the chamber 12 to the carburetor mixingchamber. A calibrated plug 48 is screwed intorthe lower end of tube 42and meters the fuel supplied to the mixing chamber. The passage 46, atits upper end, connects with a cross passage 50 formed in a bridgemember 52 which extends across the mixing chamber and is integral withthe casting 2. The passage 50 supplies fuel to the main nozzle 54 whichextends into a small venturi tube 56 positioned in the mixing chamberand extending into a large venturi 57 which forms the wall of the mixingchamber. A plug 58 having a restricted orifice therein is positioned inthe main nozzle to aid in atomizing the fuel. Air is admitted to thepassage 50 through two small passages 50 to mix with the fuel flowingtherethrough.

Positioned in the bridge piece 52 at the right of the main nozzle is asleeve 62 having a passage therethrough for idling fuel and at its rightend this sleeve is somewhat reduced in size so that it is spaced fromthe wall of the passage t), as shown in Fig. 1. The fuel which flowsthrough the sleeve 62 ultimately reaches vthe passage 64 which suppliesfuel to idling fuel supply inlets (not shown), which deliver fueladjacent the edge of the throttle valve 18. Y

The admission of air to the passage is controlled by an automaticallyoperated choke valve 70, secured to a shaft 72 suitably journalled forrotation in the wall of the casting 2. This shaft has secured to theleft end thereof, as seen in Fig. l, an arm 74 which has a horizontallyextending portion 76. The shaft 72 extends into a housing 78 which is apart of casting 2 and is provided with a removable and adjustablecover-plate 80 which may be either metal or a suitable plastic and isheld in any adjusted position by screws 82. The arm 76 at the end of thechoke shaft and cooperating parts, about to be described, are positionedin this housing.

The arm 76 is engageable by the hooked end 84 of a thermostat 86 theother end of which is secured to a pin 88 which is fixed in thecover-plate 80, as Shown in Fig. l. Upon reduction of temperature, thehooked end 84 moves counter-clockwise to engage the extension 76 of arm74 and exerts a pressure thereon to hold the choke valve in closedposition, as shown in Fig. 2. By adjustment of plate 80, the pin 88 isrotated and changes the pressure exerted by the thermostat at any giventemperature to hold the choke valve closed.

The lower end of the arm 74, as seen in Fig. 2, is pivotally connectedto a link 90 which is pivotally connected to a cross-pin 92 extendingacross a slot 93 in the right end of a piston 94slidable in a horizontalcylinder 96 integral with the housing 78 and to which the suctionmaintained in the intake passage posterior to the throttle 18 iscommunicated through a passage 98. The passage 98 may connect with thecarburetor outlet between the throttle and the manifold or with theintake passage in the manifold itself. The particular position of thisconnection is not material as long as it is on the engine side of thethrottle.

rPhe mechanism so far described is substantially the same as that shownand described in the co-pending application previously referred to.

In the device disclosed in such application the suction passagecomparable tothe passage 98 connects with the cylinder in which thesuction operated piston slides substantially at the end of suchcylinder, so that the suction, which is communicated through suchpassage, is effective on the piston throughout the whole range ofmovement of the choke valve and exerts a pulling force on the pistonuntil the valve reaches fully open position.

ln the device disclosed herein the passage 9S connects with the cylinder96 by means of an orice 100 in the wall of the cylinder. This orifice isof rectangular shape, as shown, but may be triangular or of any othershape desired, but this orice is positioned relatively close to the endof the piston when the valve is in closed position so that the' valvecannot open very far before the orice is completely blocked by the sidewall of the piston. As illustrated, the piston reaches approximately theposition designated by the dotted line A when the choke valve is about20 open. The piston 94 is slightly loose in the cylinder in which itslides so as to permit leakage of air past the piston and when thepiston reaches the dotted-line position, the area of the orifice notcovered by the piston is very little greater than this leakage space.When the parts are in such position, air can enter the cylinder atalmost the same rate as it is withdrawn therefrom, by action of thesuction passage 98. Hence, there is very little partial vacuummaintained in the D cylinder 96 when the piston reaches line A and thesuction communicated through the passage is ineffective to move thechoke valve further toward position.

The choke valve will be moved to this position by suction almostimmediately after the engine starts to run under its own power, and thisposition of the valve is that which has been found most desirable forthe beginning of the warm-up operation of some particular engine. Itmight be desirable to secure a greater or less substantially immediateopening of the choke valve for some other engine and this could beaccomplished by appropriate positioning of the orifice 100.

It also should be apparent that there may be some slight difference inthe position assumed by the valve when it first is moved by enginesuction when the engine starts to run under its own power, due to thedifference in force exerted by the thermostat at different temperatures.This difference will be very slight, however, as the valve will moveimmediately to a position where the opening and closing forces arebalanced and this will be very close to the line A with the piston endsomewhere opposite the orilce 100, and very quickly the thermostat willwarm up enough for the piston to move to` lineA. Obviously, in view ofthe foregoing, the choke valve will move, almost immediately and quiterapidly after the engine starts, to a position about 20 open, which hasbeen found desirable for some particular engines.

If the suction which is communicated through the passage 98 continuedtobe effective Yon the piston so that the valve would continue to be movedby the effect of suction during the warm-up period, it has been foundfor aannam@ some engines that the vmovement would be vtoo rapid and themixture would become too llean lfor ventirely satisfactory operation. Itis, therefore, desirable .to `retard the further opening movement ofthevalve relative to its rate of movement at the beginning-of suchmovement, sothat its opening from .20 -tosomepredetermined position,more than open, isrelatively slow. Therefore, the oriiice 100 is sopositioned that .after the valve opens about 20 the suction becomessubstantially ineffective and the subsequent movement ofthe valve iscontrolled by the rate at which the thermostat is heated.

To this end, Lthe :passage '98 connects `with Va passage 102 formed inthe casting 2 xwhich leads @to the interior of the housing 78 and also apassage 104 formed in a threaded nipple V106 extendingfrom the housing78 'communicates with 'the interior-thereof. This nipple may bepositioned at any point on the housing where it gives the best results.Connected to the nipple 106 is a conduit 108 leading to a source of hotair (not shown), for example, a stove on the exhaust manifold.

The engine suction is communicated through passage 102 to the interiorof housing 78 and draws heated air through passage 104 through thehousing to heat the thermostat. During the warm-up period, after thepiston has reached line A, the heated air passing through housing 78progressively heats the thermostat so that the hooked end 84 movesclockwise and away from the extension 76 of arm 74. As the end of thethermostat so moves, the choke valve is moved toward open position, at arate which is determined by the thermostat, by the force exerted by theentering air directly on the choke valve 70. This movement is relativelyslow until the choke valve reaches a predetermined open position whenthe rate of movement of the choke valve is considerably increased andthe valve continues to move at the increased rate until it reaches fullopen position.

To effect this increased rate of movement, the piston 94 is cut away onthe lower side thereof, as indicated at 110 and this cut-away portion ofthe piston is brought into registry with the orifice 100 when the chokevalve is about 55 open. As soon as this occurs, the eect of suctioncommunicated to the interior of the housing 78 is much increased andmuch larger quantities of heated air per unit of time are drawn throughhousing 78. This eiects heating of the thermostat more rapidly after thechoke valve is opened to the extent referred to and more rapid openingmovement of the choke valve is effected from that point to its full openposition, than its movement from 20 open to the position at which thecutaway portion 110 becomes effective. l

It will be apparent from the foregoing that in the device disclosed thechoke valve is moved very rapidly by the eect of engine suction, whenthe engine starts to run under its own power, to a position about 20open, the effect of engine suction is then substantially eliminated, thevalve is then moved more slowly at a rate controlled primarily by thethermostat to a position about 55 open, and finally is moved morerapidly from 55 open to full open position, this being effected by morerapid heating of the thermostat after the valve is opened to thatextent. These movements of the valve could be brought about at dilerentpoints in its operating range by changing the position of the orifice100 or changing the length of the cut-away part 110 of the piston. Bysuitable dimensioning of the parts, substantially any desired rate ofmovement of the choke valve can be obtained at different parts of itsoperating range.

It may be said that, upon acceleration during the warmup period, theoperation of the device disclosed herein is somewhat different from theconventional automatic choke. ln the latter, when the throttle is openedto eect acceleration, the choke moves somewhat toward closed position,due to the drop in suction effective on the piston corresponding topiston 94. In this device, since the suction is substantiallyineffective on the piston after the valve `is .20 i open, v-the 'drop inYsuction in passage 98 `when' sthe throttle iszopened is substantiallyvwithout etfectland the Yvalve will probablybe opened-slightly due totheincrease in pressuredilferential across the vvalve 70 itself. Therefore,-the -desired mixture vfratio for .acceleration must be effectedby'theaccelerator pump which is probably `beneficial because tthe :pumpis morefeasily =and;accurately.c'on trollable.

While the Vembodiment of the .present invention 'as herein disclosedconstitutes :a ypreferred form, itis to kbe understood that other .formsmightfbefadopted.

What is claimed is as follows:

=l. In a charge 'fortningrdevice for aninternal combustionrengineAhaving a-constant level fuel supply chamber, anlintakepassagehavingfuel and air inletsand a mixture outletfor lsupplyi'ng lacombustible mixture .to lsaid engine, a :throttle -valvelfor,c-:ontrolling' fthe itlow of ksaid mixture, an unbalanced chokevalve operable in response to variations in the intake passage forcontrolling the admission of air through said inlet; mechanism forautomatically controlling the operation of said choke valve comprising athermostat operable to exert a force tending to hold said valve closedupon a reduction in temperature, a suction operated member connected tosaid valve and operable to move said valve toward open position upon anincrease in suction, a conduit to communicate the engine suction to saidmember, said conduit being so positioned that it is blocked by saidmember when the valve reaches a partially open position, a housing inwhich the thermostat is positioned, a source of heated air, a suctionpassage communicating with said housing and effective to draw heated airfrom said heat source through said housing to progressively heat thethermostat whereby the valve closing force of the thermostat isprogressively reduced and the choke valve is moved further toward openposition only by the suction effective on the valve itself after saidconduit is blocked by said suction operated member, and a second meansfor drawing heated air through said housing which is rendered effectivewhen the choke valve reaches a predetermined open position to effectmore rapid heating of the thermostat so as to bring about more rapidmovement of the valve toward open position after it has been opened to apredetermined extent.

2. In a charge forming device for an internal combustion engine having aconstant level fuel supply chamber, an intake passage having fuel andair inlets and a mixture outlet for supplying a combustible mixture tosaid engine, a throttle valve for controlling the ow of said mixture, anunbalanced choke valve operable in response to variations in the intakepassage for controlling the admission of air through said inlet;mechanism for automatically controlling the operation of said chokevalve comprising a thermostat operable to exert a force tending to holdsaid valve closed upon a reduction in temperature, a suction operatedpiston slidable in a cylinder and operatively connected to the valve soas to move the valve toward open position upon an increase of suction, asuction conduit connected to said cylinder intermediate its ends andadapted to be blocked by said piston when the valve is moved topartially open position so that the piston is rendered ineffective tomove the valve further toward open position, a housing surrounding thethermostat, a source of heated air, a constantly open passage connectingsaid conduit with the housing and effective to draw heated air from theheat source through the housing to heat the thermostat and reduce itsvalve closing force so as to permit further opening of the valve by thesuction effective on the valve itself, and a second normally closedpassage connecting said conduit with the housing, said last named meansbeing rendered effective after the choke valve reaches a predeterminedopen position.

3. In a charge forming device for an internal combustion engine having aconstant level fuel supply chamber, an intake passage having fuel andair inlets and a mixture outlet for supplying a combustible mixture tosaid engine, a`throttle valve for controlling the flow of said mixture,an unbalanced choke valve operable in response to variations in theintake passagefor controlling the admission of air through said inlet;mechanism for automatically controlling the operation of said chokevalve comprising a thermostat operable to exert a force tending to holdsaid valve closed upon a reduction in temperature, a suction operatedpiston slidable in a cylinder and operatively connected to the valve soas to move the valve toward open position upon an increase of suction, asuction conduit connected to said cylinder intermediate its ends andadapted to be blocked by said piston when the valve is moved topartially open position so that the piston is rendered ineffective tomove the valve further toward open position, a housing surrounding thethermostat, a source of heated air, a constantly open passage connectingsaid conduit with the housing and eiective to draw heated air from saidheat source through the housing to heat the thermostat and reduce itsvalve closing force so as to permit further. opening of the valve by thesuction effective Von the valve itself, said piston having a passage inthe wall l0 position as the valve approaches its fully open position.

References Cited in the le of this patent UNITED STATES PATENTS WinklerSept` 26, 1950 v2,719,706 Winkler Oct. 4, 1955

